1. Field of the Invention
This invention relates to a battery breaker having a structure of bringing or separating a movable contact into contact with or from a fixed contact by the spring action of a movable piece or the warping action of a bimetal.
2. Description of the Prior Art
A description will now be given of two kinds of conventional breakers each provided with a movable piece having elasticity and a bimetal with reference to FIGS. 48 to 50.
FIG. 48 is a cross-sectional view showing a breaker (a temperature switch), and FIG. 49 is an exploded perspective view showing a main part of the breaker of FIG. 48.
Reference numeral 5 denotes a housing composed of a mounting base 50 and a cover 51 covering the upper surface of the mounting base 50. A fixed contact 60 is mounted to the inner bottom surface of one end of the mounting base 50, and an end of a terminal 61 extending from the housing 5 outwards is connected to the bottom surface of the fixed contact 60.
A band plate-shaped movable piece 63 having elasticity is mounted to the other end of the mounting base 50 such a way that the tip end of the movable piece protrudes into the housing 5 toward the fixed contact 60. The movable contact 62 fixed to the tip end of the movable piece 63 is in contact with the fixed contact 60 by the spring action of the movable piece 63. The movable piece 63 has semicircular-shaped notches 65, 65 in opposite side portions on the fixed end side, and these notches 65, 65 are brought into engagement with pins 52, 52 provided on the inner bottom surface of the mounting base 50. The movable piece 63 also has a downwardly convex portion 64 such that the tip end of a bimetal 54 which will be described later may be brought into contact with the convex portion when the bimetal is warped to make the snap action. The movable piece 63 further has a terminal 66 as one body at a portion extending from the housing 5 outwards.
The bimetal 54 having an upwardly convex curved surface is placed between the inner bottom surface of the mounting base 50 and the movable piece 63. In this place, the bimetal is warped at a predetermined working temperature to push up the movable piece 63 by the snap action resulting from warping of the bimetal for separating the movable contact 62 from the fixed contact 60.
The bimetal 54 is formed by placing a main bimetal 54a and an auxiliary bimetal 54b having a working temperature different from that of the main bimetal one over the other. The main bimetal 54a and the auxiliary bimetal 54b have semicircular-shaped notches 56, 56, 57, 57 on the opposite sides of the base ends respectively, and these notches 56, 57 are brought into engagement with the corresponding pins 52, 52.
The mounting base 50 has a projection 53 on the inner bottom surface at a position corresponding to the warping center of the bimetal 54. The projection 53 is inserted through a central through hole 55 of the auxiliary bimetal 54b until the center portion of the main bimetal 54a is brought into contact with the projection 53. The constitution described the above makes it possible to reduce one-sidedly biased distribution of bending stress of the bimetal 54.
FIG. 50 is a cross-sectional view showing another conventional breaker (a temperature switch).
A housing 7 is composed of a mounting base 70 and a cover 71 covering the upper surface of the mounting base, and a fixed contact 80 is mounted to the inner bottom surface of one end of the mounting base 70 of the housing 7. An end of a terminal 81 extending from the housing 7 outwards is connected to the bottom surface of the fixed contact 80.
A band plate-shaped movable piece 83 having elasticity is mounted to the other end of the mounting base 70 such that the tip end of the movable piece protrudes into the housing 7 toward the fixed contact 80. The movable piece 83 has a through hole in a position close to the fixed end, and a guide pin 74 provided on a convex portion 73 of the inner bottom surface of the mounting base 70 is inserted through this through hole. In FIG. 50, there is shown the state of the breaker when a bimetal 72 which will be described later is warped to separate a movable contact 82 fixed to the tip end of the movable piece 83 from the fixed contact 80 by the snap action of the bimetal. However, the movable contact 82 is normally in contact with the fixed contact 80 by the spring action of the movable piece 83. The movable piece 83 has a downwardly convex portion 84 such that the tip end of the bimetal 72 is brought into contact with the convex portion when the bimetal is warped to make the snap action. The movable piece 83 also has a terminal 85 as one body at a portion extending from the housing 7 outwards.
The bimetal 72 having an upwardly convex curved surface is placed between the inner bottom surface of the mounting base 70 and the movable piece 83. In this place, the bimetal is warped at a predetermined working temperature to push up the movable piece 83 by the snap action resulting from warping of the bimetal to separate the movable contact 82 from the fixed contact 80.
The bimetal 72 has a through hole in a position close to the base end, and the guide pin 72 provided on the inner bottom surface of the mounting base 70 is inserted through this through hole. A base end 72a serving as the warping center of the bimetal 72 is brought into engagement with the convex portion 73 on the inner bottom surface of the mounting base 70. Since the bimetal 72 has the warping center located at the base end 72a (at the right end of the bimetal in FIG. 50) as described the above, a free end (the left end of the. bimetal in FIG. 50) of the bimetal 72 is shifted upwards when the bimetal 72 is warped at the predetermined working temperature. Then, the bimetal 72 pushes up the movable contact 82 through the upwardly shifted free end to separate the movable contact 82 from the fixed contact 80.
The conventional breaker shown in FIGS. 48 and 49 presents the following problems.
Since there are the needs of forming the notches 65 in the movable piece 63 and the notches 56, 57 in the bimetals 54a, 54b and also bringing these notches into engagement with the pins 52, 52, a large number of assembly processes, the high manufacturing cost and besides, the complicated structure are required, resulting in a limitation to demands for miniaturization of the battery breaker.
Since the notches 56, 57 of the bimetals 54a, 54b are brought into engagement with the pins 52, 52, the operating performance of the bimetal is degraded. Besides, because of the need for the notches 56, 57 for the bimetal, the warping action of the bimetal easily causes cracks in the bimetal through the notches 56, 57.
The conventional breaker shown in FIG. 50 presents the following problems.
A large number of processes such as formation of the holes in the movable piece 83 and the bimetal 72 and insertion of the guide pin 74 through the holes are required, resulting in an increase in manufacturing cost.
Since the warping center of the bimetal 72 is located at the base end 72a, and only the free end of the bimetal 72 is warped, the operating performance of the bimetal is degraded. From the similar reasons, the bimetal needs to be increased in size to allow the bimetal to act as desired, resulting in a limitation to demands for miniaturization of the battery breaker.
It is an object of the present invention to provide a battery breaker, which may be manufactured to have a smaller size.
Another object of the present invention is to provide a battery breaker, which requires more simple structure for separating a movable contact from a fixed contact depending on a smaller operating amount of a bimetal.
A battery breaker according to the present invention comprises a case, a fixed contact, which is mounted to the inner bottom surface of one end of the case and is connected to a terminal extending from the case outwards, an elastic movable piece, which is mounted such that its tip end protrudes into the case through the other end of the case and allows a movable contact provided at the above tip end to bring into contact with the fixed contact by the spring action, and a convex curved surface-shaped bimetal, which has a warping center located in the substantial center or at a position slightly one-sided from the center, is placed between the movable piece and the inner bottom surface except for the above one end of the case so as to cover a projection provided on the above inner bottom surface without interference of an outer periphery of the bimetal with the inner side surfaces of the case, and is warped at a predetermined working temperature to push up the movable piece for separating the movable contact from the fixed contact, wherein the movable piece has downwardly convex portions brought into contact with the opposite ends of the bimetal when the bimetal is warped.